x-session-id

x-session-id is a variable defined in `C source code'.
Its value is

nil

Documentation:
The session id Emacs got from the session manager for this session.
Changing the value does not change the session id used by Emacs.
The value is nil if no session manager is running.
See also `x-session-previous-id', `emacs-save-session-functions',
`emacs-session-save' and `emacs-session-restore'."